1. Field of the Invention
The present invention relates to a radio communication device and a method of measuring a distance, and more particularly, is suitably applied to a potable telephone in a cellular digital portable telephone system.
2. Description of the Related Art
A portable telephone communicates with another terminal via a base station which is the nearest to the portable telephone. And even if the own terminal and the companion terminal exist within the same area, a base station is absolutely necessary to perform communications via.
That is, since the portable telephone does not have an interface for radio communications which is used for communicating with another terminal other than the base station, it has to communicate via the base station when communicating with a companion terminal.
By the way, such a portable telephone has to communicate with a companion terminal via the base station. Therefore, even if the terminal exists in the same area as the portable telephone at the time of meeting, the base station has to be used to call the companion terminal over a public circuit network so that they can inform each other of their positions by means of audio communications.
In addition, the portable telephone is difficult to exactly know whether the companion terminal is xe2x80x9cgetting closerxe2x80x9d or xe2x80x9cgetting fartherxe2x80x9d while they move, which causes a problem in its usability.
In view of the foregoing, an object of this invention is to provide a radio communication device and a method of measuring a distance which offer excellent usability and are capable of easily detecting a distance and a positional relation between the device and a target for measurement.
The foregoing object and other objects of the invention have been achieved by the provision of a radio communication device which directly transmits via a radio communication means a predetermined measurement signal which is used for calculating a distance between a specific target for measurement and its current position, receives a response signal in response to the measurement signal transmitted from the target for measurement, and then calculates the distance between its current position and the target for measurement, based on the response signal and the measurement signal, so that the distance and the positional relation between the target for measurement and its device can be easily calculated by directly communicating the measurement signal and the response signal with the target for measurement, not via a base station.
In addition, in the present invention, a radio communication device directly transmits standard time information showing a transmission time toward a specific target for measurement, which is used for calculating a distance between its current position and a target for measurement, to the target for measurement, receives reception time information of the standard time information, which is transmitted from the target for measurement and then, calculates the distance between the current position and the target for measurement based on the standard time information and the reception time information. Thereby, the radio communication device can easily calculates the distance and the positional relation between the own device and the target for measurement by directly communicating the standard time information and the reception time information, not via a base station.
Furthermore, in the present invention, a radio communication device directly transmits standard time information indicating the transmission time toward a specific target for measurement, which is used for calculating a distance between its own current position and the target for measurement, to the target for measurement, receives reception time information of the standard time information, which synchronizes with the standard time information in absolute time, from the target for measurement and then, calculates the distance between the current position and the target for measurement based on the standard time information and the reception time information. Thereby, the distance and the positional relation between the own device and the target for measurement can be easily and accurately calculated by directly communicating the standard time information and the reception time information which synchronize to each other, with the target for measurement, not via a base station.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.